This invention relates to phased array antennas, and more particularly to a three dimensional packaging architecture for forming a high frequency, electronically steerable phased array antenna module with a greatly reduced number of external interconnecting elements.
Phased array antennas are comprised of multiple radiating antenna elements, individual element control circuits, a signal distribution network, signal control circuitry, a power supply and a mechanical support structure. The total gain, effective isotropic radiated power (xe2x80x9cEIRPxe2x80x9d) (with a transmit antenna) and scanning and side lobe requirements of the antenna are directly related to the number of elements in the antenna aperture, the individual element spacing and the performance of the elements and element electronics. In many applications, thousands of independent element/control circuits are required to achieve a desired antenna performance.
A phased array antenna typically requires independent electronic packages for the radiating elements and control circuits that are interconnected through a series of external connectors. As the antenna operating frequency (or beam scan angle) increases, the required spacing between the phased array radiating elements decreases. As the frequency increases, the required spacing becomes smaller. As the spacing of the elements decreases, it becomes increasingly difficult to physically configure the control electronics relative to the tight element spacing. This can affect the performance of the antenna and/or increase its cost, size and complexity. Consequently, the performance of a phased array antenna becomes limited by the need to tightly package and interconnect the radiating elements and the element electronics associated therewith with the required number of external connectors. As the number of radiating elements increases, the corresponding increase in the required number of external connectors (i.e., xe2x80x9cinterconnectsxe2x80x9d) serves to significantly increase the cost of the antenna.
Additionally, multiple beam antenna applications further complicate this problem by requiring more electronic components and circuits to be packaged within the same module spacing. Conventional packaging approaches for such applications result in complex, multi-layered interconnect structures with significant cost, size and weight.
FIG. 1 illustrates one form of architecture, generally known as a xe2x80x9ctilexe2x80x9d architecture, used in the construction of a phased array antenna. With the tile architecture approach, an RF input signal is distributed into an array in a distribution layer 10 that is parallel to the antenna aperture plane. The distribution network 10 feeds an intermediate plane 12 that contains the control electronics 14 responsible for steering and amplifying the signals associated with individual antenna elements. A third layer 16 includes the antenna elements 18. The third layer 16 comprises the antenna aperture and typically includes a large plurality of closely spaced antenna elements 18 which are electronically steerable by the control electronics 14. Output signals radiate as a plurality of individually controlled beams from antenna radiating elements 18.
With the tile architecture approach described in FIG. 1, the radiating element 18 spacing determines the available surface area for mounting the electronic components 14.
The tile architecture approach can be implemented for individual elements or for an array of elements. An important distinction of the traditional tile architecture approach is its ability to readily support dual polarization radiators as a result of its coplanar orientation relative to the antenna aperture. Individual element tile configurations can also allow for complete testing of a functional element prior to antenna integration. Ideally, the tile configuration lends itself to most manufacturing processes and has the best potential for low cost if the electronics can be accommodated for a given element spacing. This configuration also requires discrete interconnects for each layer in the structure, where the number of interconnects required is directly in accordance with the number of radiating elements of the antenna. Additionally, the mechanical construction of the individual tiles in the array typically contributes to limitations on the minimum element spacing that can be achieved.
A tile architecture configuration for a phased array antenna can also be implemented in multiple element configurations. As such, the tile architecture approach can take advantage of distributed, routed interconnects resulting in fewer components at the antenna level. The tile architecture approach also takes advantage of mass alignment techniques providing opportunities for lower cost antennas. The multiple element configuration, however, does not support individual element testing and consequently is more severely impacted by process yield issues confronted in the manufacturing process. Conventional enhancements to the basic tile architecture approach have involved multiple layers of interconnects and components, which increases antenna cost and complexity.
FIG. 2 illustrates a different form of packaging architecture known generally as a xe2x80x9cbrickxe2x80x9d or xe2x80x9cin-linexe2x80x9d packaging architecture. With the brick architecture, the input signal is distributed in a 1xc3x97N feed layer 20. This distribution layer feeds N 1xc3x97M distributions 22-36 that are arranged perpendicular to the 1xc3x97N feed layer 20 and the antenna aperture plane. With the brick architecture, the radiating elements 38 on each distribution layer 22 are arranged in line with the element electronics 38 (shown in highly simplified form). Because of the in-line configuration of the radiating elements 38 and their orthogonal arrangement to the antenna aperture, the traditional brick architecture approach is typically limited to single polarization configurations. Like the tile architecture approach, however, the radiating elements can be packaged individually or in multiple element configurations as shown in FIG. 2. External interconnects are used between the input feed layer 20 and the distribution layers 22. Typically, the brick architecture approach results in an antenna that is deeper and more massive than one employing a tile architecture approach for a given number of radiating elements. The brick architecture approach, however, can usually accommodate tighter radiating element spacing since the radiating element electronics are packaged in-line with the radiating elements 38. The ability to test individual radiating elements 38 prior to antenna integration is limited, with a corresponding rework limitation at the antenna level.
The assignee of the present application is a leading innovator in phased array antenna packaging and manufacturing processes involving modified tile and brick packaging architectures. The prior work of the assignee in this area is described in U.S. Pat. No. 5,886,671 to Riemer et al, issued Mar. 23, 1999 and U.S. Pat. No. 5,276,455 to Fitzsimmons et al, issued Jan. 2, 1994. The disclosures of both of these patents are hereby incorporated by reference into the present application. While the approaches described in these two patents address many of the issues and limitations of tile and brick packaging architectures, these approaches are still space limited as the frequency increases.
Accordingly, there is a need for a packaging architecture for a phased array antenna module which permits even closer radiating element spacing to be achieved, and which allows for even simpler and more cost efficient manufacturing processes to be employed to produce a phased array antenna.
More specifically, it is an object of the present invention to provide a packaging architecture for forming a phased array antenna module which significantly reduces the physical space required for interconnects between the electronics and the radiating elements of the antenna, as well as the need for external interconnecting elements for forming the transmission feed lines of the antenna module.
It is still another object of the present invention to provide a packaging architecture for a phased array antenna module which significantly simplifies the manufacturing of the antenna module, and which allows the antenna to be adapted for various implementations which require the radiating elements thereof to be disposed in various angular orientations relative to other portions of the antenna module.
The above and other objects are provided by a phased array antenna module employing a three dimensional packaging architecture. The antenna module of the present invention generally comprises a conformable circuit element forming a substrate having integrated, monolithic transmission lines, radiating elements and distribution feed lines. Since the conformable circuit element can be formed in a variety of shapes during assembly, the circuit element can be adapted for implementation in a wide variety of antenna configurations to suit specific applications.
The conformable circuit element comprises a multi layer flexible circuit element to which a plurality of electronic elements, typically monolithic microwave integrated circuits (MMICs) and application specific integrated circuits (ASICs), can be coupled. The radiating elements are formed directly on the conformable circuit element together with a corresponding plurality of integrated, monolithic transmission lines which electrically couple the radiating elements with the element electronics. A plurality of output pads are also formed on the conformable circuit element in communication with the monolithic feed transmission lines. Optionally, an integrated power combiner/splitter may be formed on the substrate in communication with the circuit elements. Also, flip chip MMICs and ASICs can be secured directly on the conformable circuit element if desired.
Since the conformable circuit element is flexible, it can be readily adapted for use in a variety of implementations. The integrated radiating elements, monolithic transmission lines and monolithic feed transmission lines eliminate the need for external interconnects, thus enabling the radiating elements to be packaged with even less spacing being required between the elements. Consequently, a receive and/or transmit antenna can be formed using the packaging and architecture of the present invention to incorporate a large number of radiating elements, associated electronics and interconnecting elements in a very compact and cost efficient assembly.
The flexibility afforded by the conformable circuit element allows the radiator elements to be placed at various angular orientations relative to the remainder of the conformable circuit element. This feature also enables the conformable circuit element to be secured to other components, such as a central core element, such as when forming a waveguide radiator.
As will be appreciated, the packaging architecture of the present invention also enables a receive and/or transmit antenna module to be constructed even more cost effectively than with previous variants of the brick and tile architecture approaches. The reduced manufacturing cost enables antenna modules constructed in accordance with the present invention to be used in an even greater number of applications where the use of a phased array antenna requiring hundreds or thousands of radiating elements would have previously been cost prohibitive.